(A) Field of the Invention
The present invention relates to an apparatus for testing bonding strength of electrical connections and a calibration device for the same, and more particularly, to an apparatus equipped with a rotational test head having at least two probes for testing the bonding strength of the electrical connection and a frictionless calibration device for the same.
(B) Description of the Related Art
Semiconductor devices have sites for the bonding of electrical conductors thereto; such sites typically comprise partly spherical deposits of gold or solder, collectively known as balls. It is necessary to test the mechanical strength of the bonding between the gold or solder balls and the substrate in order to give confidence that the bonding method is adequate, and that the bonding strength is sufficient. It has been proposed to test such balls by applying a flat shear tool to one side thereof. In order to avoid friction caused by the tool rubbing on the surface of the substrate, it is necessary for the tool to be just above the substrate surface.
U.S. Pat. No. 6,341,530 discloses a device for testing the force to shear a deposit of solder or gold from a substrate, for deposits having a diameter in the range 50-100 mm and being for the bonding of electrical conductors. A shear tool has a semi-cylindrical cavity, which closely approximates to the mean diameter of a range of substrates. This tool is adapted to re-shape substrates for a better fit, re-shaping occurring over 30% or less of the circumference of a deposit, and to a depth of 10% or less of the diameter of the substrate.
US 2004/0103726 discloses a tool to be installed into a test module of a bond test system to provide the capability to directly view a bond shear test. This capability enables a vision system camera coupled to magnifying optics to provide real time viewing, image capture, and vision guided automation for more effective analysis, additional analytic capability and improved ergonomics. This greatly enhances the utility of the shear test function of the bond test system.
In addition to the shear test for the bonding strength of the balls, the semiconductor devices are also required to conduct a pull test for the bonding strength of the bonding wires. However, the above-mentioned references can conduct only the shear test, not the pull test. Furthermore, the shear force is applied to the balls in the shear test, and the applied force is not stopped until the ball is removed; the pull force is applied to the boding wires in the pull test, and the applied force is not stopped until the bonding wires break off, i.e., the shear test and the pull test are destructive tests, which can not be repeated at the same condition. Therefore, it is necessary to calibrate the applied force of the test tool.